Wealthy Alexander Moore and working-class Jerry Crowe are childhood friends and in 1914 find themselves in the same Army unit - Alex as an officer and Jerry as a private. They still remain close, however, until Jerry is court-martialed for desertion, and Alex is put in charge of the firing squad.

A Victorian gentleman hopes to find his long-lost son, who vanished while searching for a mysterious Viking community in a volcanic valley somewhere in uncharted Arctic regions. The gentleman puts together an expedition team to go on the search, but when they reach their destination they must escape from some Viking descendants who will kill to keep their existence a secret.

An unknown thief steals an important naval treaty from the office of Mr. Percy Phelps, a Foreign Office clerk. Phelps's distress gives him a brain fever that lasts for nine weeks. As he begins to recover, he writes to his old schoolmate, Dr. Watson, begging him to invite Sherlock Holmes to investigate the matter and find the treaty. Otherwise, his honor and happiness are gone forever. Holmes takes up the case with zest, but gives Phelps no false hopes. The mystery is as dark and tangled as any he has known.